Further studies will be carried out to determine whether the cyclic nucleotides may mediate effects of prolactin on the metabolism of the mammary gland. Levels of cyclic AMP and cyclic GMP will be measured in tissues treated with prolactin. In addition, further studies will be carried out to determine whether prolactin affects the activities of the following enzymes; guanyl cyclase and the phosphodiesterases. Experiments will also be carried out to determine whether the prostaglandins may be an intracellular mediator for the actions of prolactin on the mammary gland. Attempts will be made (1) to mimic the actions of prolactin with exogenous prostaglandins and (2) to measure whether prolactin affects the level of prostaglandins in the mammary gland.